A lot of building science is pretty theoretical. No matter how much research you do, at the end of the job, most of the work is hidden in the walls. Unless you come back to do renovations or worse, get a dreaded call back for something gone seriously wrong, you rarely get the opportunity to see how your work performs. I am not talking about cosmetic details like nail holes that don’t get filled or rough edges that didn’t get sanded. I’m talking about how well materials hold up to the heat or how well you have managed moisture movement through the walls, either as precipitation working its way in, or the more mysterious way that water vapor works its way out (or inwards in some climates).
This moisture is driven by vapor pressure, which can drive water molecules through most any material given the proper humidity and heat differentials—something a sauna has a lot of.
I learned about vapor pressure when I realized that my hollow steel yard sculptures inexplicably filled up with water. My welds are very solid and water-tight, but somehow, moisture was penetrating the steel, condensing, and not getting out. Cutting holes in the bottoms to let trapped water out solved that problem. There’s a bit of molecular science involved here, but suffice it to say, that vapor pressure is very strong—strong enough that when I throw water on the hot rocks, my sauna door pops open as if the löyly has scared a ghost out of hiding.
Thinking about all of this has left me wondering what is happening in my sauna walls? Am I doing a good job? Is the insulation holding up? Is water getting trapped?
Yesterday, I had to do some retrofitting on the first mobile sauna I built in 2013. I exchanged the Scandia gas heater for a wood burner and got to peer into the dark interior of the walls. This is a sauna that has seen heavy and very hot (200°+) usage. The walls were built with cedar inside and out with only a 1″ layer of foil-faced polyioscyanurate foam board between the studs.
Here is what I found:
There was no damage from trapped moisture, and the foam board looked as good as new; the foil facing was still shiny!
There was some hi-temp fiber-fax insulation used around the gas heater. A rodent had gotten into this (despite my filling gaps around the gas line with steel wool) and made a stinky little nest.
So, this confirmed my use of the polyisocyanurate board, which has a service temperature of 250°F, and verified my disdain of fiberglass-type materials (rodents love it).
On my desk, I have a piece of expanded polysytrene foam (EXP) I pulled out of a failed sauna I was asked to repair. It looks like one of my steel sculptures from my Landform series—a flowing, green landscape (of melted plastic). Its service temp is listed as 150° F. All materials have material data sheets, usually available on the manufacturers web pages. I consult these whenever I am unsure about materials, especially given that the extremes of the sauna are like the extremes NASA engineers have to deal with.
Clearly, there is a correlation between science and reality, even if it is happening unseen inside the walls of your sauna. So when choosing materials, listen to the science, learn from observation, and don’t just buy the cheapest materials or use only the easiest approach.
Consult with the experts. Sometimes, there is more to it than meets the eye.
The New England coast is beautiful and varied, from the dramatic rocky shores of Maine to the sandy beaches of Cape Cod to the rocky moraine of Long Island’s north shore. The one thing New England’s coastal waters are not is warm. I remember swimming in Maine when I was in art school in Portland: I would get all hot and sweaty by running or biking to the beach and jump in and swim a brisk few hundred yards, to the astonishment of onlookers who dared not go past their knees. For most people the swimming season in Maine consists of two weeks in August.
It is no wonder that my last several mobile saunas have found homes near the coast—what a perfect way to extend the swimming season! Cold water and saunas traditionally go together. Ideally the sauna is situated so one can plunge into a lake, pond, stream, or ocean after each round. With a sauna on wheels, you can pull up to your favorite dipping spot and indulge yourself anytime of year. There is nothing like the thrill of jumping through a hole in the ice or plunging next to a waterfall in the whiteness of winter.
The mobile unit is fairly clandestine—once the stove reaches temperature, the chimney smoke is invisible; no one will suspect you are nearly naked inside, basking until you burst out and head for the water. I haven’t had the pleasure of sauna-ing next to the ocean, but one of these days, I’ll have to travel back to Higgin’s Beach in Maine, sauna in tow, and give onlookers a thrill as I defy the icy winter water with a post-sauna dip.
You ask how or why electric mobile sauna? There are a number of reasons why going mobile makes sense, especially if you rent. No permits or special permissions are needed. You just park it in your yard and use it. You can take it with you on vacations or just for a Saturday down by the lake; you can even enter it in a parade. But why electric? Electric is no longer the inefficient dark horse of the energy world that it once was. It can be generated cleanly by wind or solar and is cheaper, cleaner, and easier to use than gas or oil. Although any purist will tell you a wood-burning sauna is the real deal, in some places, wood is not so easy—firewood may be hard to come by and difficult to store, and your neighbors may be too close for comfort or offended by the occasional whiff of smoke. Since I’ve eliminated gas burners from my repertoire (for reasons I won’t go into here), an electric mobile sauna is the next best thing. All you need is a place to plug it in.
When clients ask me to create a sauna, they often push me to do things I might have never considered doing. I’ve gotten requests to make saunas in spaces I thought were too tiny, on trailers, deep in the woods next to a pond, or to convert a cheap shed or laundry room. The most recent project to leave the shop is an electric mobile sauna. The owner has a Tesla electric car, so an electric sauna just seemed to make sense. The colors were more of an emotional choice: I painted it Sea Reflections blue like the ocean, where she likes to swim all year, with a Bonfire Red door to beckon her into the warmth of its interior and Vanilla Ice Cream trim because, well, who doesn’t like ice cream, especially after a sauna?
The how is simple: an 8 KW heater with a standard RV type hook up and a fifty-foot, very-heavy extension cord that connects to a standard car charging port (or special outdoor outlet). This will also work in many campgrounds with RV hookups. In a pinch, it can also be run off an 8500-watt generator.
This sauna also has a solar-powered low-voltage lighting system, just so there can always be light and because low-voltage systems are safer and more versatile than 120-volt lighting. I’ve been using these in some mobile wood burners and freestanding units. The neat little solar panel is a conversation starter; people are suddenly aware that the unit is more than a fancy tool shed trailer. When I tell them it’s an electric sauna, the little 25-watt solar panel gets a second glance.
I envision a fully solar electric sauna next (but probably won’t consider doing unless a client pushes me). It would have to use Tesla’s 270-pound Powerwall home battery, which has an 8kw output capacity. I imagine the entire sauna roof would a have to be a solar panel, but I haven’t done the engineering on this. This would not be cheap, but if someone out there who wants to be the first…. give me a call.
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